Transducer for generation and detection of shear waves

Abstract

An improved transducer for generating and detecting shear waves using pielectric bimorph elements. A plurality of pairs of bimorph elements are formed by rigidly attaching together two individual lengths of piezoelectric material with each dimensioned to provide a length and width substantially greater than its thickness. The plurality of bimorph pairs are mounted in a configuration such that each pair is separated by a layer of high compliance material with the electrical polarization of each piezoelectric element pointing in the same direction. Electrical potential applied simultaneously to the electrodes of the individual pairs causes the entire end face of the transducer to perform a shearing motion which will generate or detect acoustic waves in materials in contact with the face.

What is claimed and desired to be secured by Letters Patent is: 
     
       1. An improved transducer for generating and detecting acoustical energy propogating in materials having a low acoustical impedance comprising: a plurality of deformable bimorph elements, each of said elements being formed by two individual deformable members polarized in the same direction;   high compliance means coupled to said bimorph elements for separating each of said elements, said elements being arranged such that the polarization of all of the members is oriented in the same direction; and   means for providing electrical connections to each of said elements, said electrical connections and high compliance means being constructed and coupled to said elements in such manner as to enable the generation and detection of shear waves through said bimorph elements.   
     
     
       2. The transducer of claim 1 wherein each of said deformable members has a length and width substantially greater than its thickness. 
     
     
       3. The transducer of claim 1 wherein each of the deformable members comprises a piezoelectric material. 
     
     
       4. The transducer of claim 3 wherein each of the piezoelectric members has a generally rectangular plate configuration having two pairs of opposed parallel planar surfaces and wherein said means for providing electrical connections comprises an electrically conductive coating applied to one pair of the opposed planar surfaces of each piezoelectric member, to form electrode surfaces said bimorph elements being constructed by rigidly attaching pairs of the piezoelectric members along an electrode surface to form a common electrode between each pair. 
     
     
       5. The transducer of claim 4 wherein the polarization of each piezoelectric member is oriented in a direction perpendicular to the planar electrode surfaces and wherein the plurality of piezoelectric members are arranged to form a substantially planar end face parallel to the direction of polarization. 
     
     
       6. The transducer of claim 5 wherein the means for separating comprises a substantially uniform layer of high compliance material rigidly attached to the electrode surfaces of adjacent bimorph elements. 
     
     
       7. The transducer of claim 4 further comprising: a source of alternating electrical potential;   means for coupling one terminal of said source to each of the common electrodes of said bimorph element; and   means for coupling the other terminal of said source to each of the remaining electrode surfaces deposited on the piezoelectric members.   
     
     
       8. An improved apparatus for generating acoustical energy comprising: a transducer including, a plurality of deformable bimorph elements, and   high compliance means coupled to said elements for separating each of said elements, said high compliance means being constructed and coupled to said elements to form a surface capable of providing a shearing motion; and     means coupled to said transducer for causing the same to generate shear waves.   
     
     
       9. The apparatus of claim 8 wherein each of said bimorph elements comprises two individual piezoelectric members each having a length and width substantially greater than its thickness. 
     
     
       10. The transducer of claim 9 wherein each of the piezoelectric members has an electrical polarization oriented in the same direction as the polarization of all members in the transducer. 
     
     
       11. The apparatus of claim 9 wherein each of the piezoelectric members has a generally rectangular plate configuration having two pairs of opposed parallel planar surfaces and wherein said means for causing said transducer to generate shear waves comprises; an electrically conductive coating applied to one pair of the opposed parallel surfaces of each piezoelectric member, each bimorph element being constructed by rigidly attaching a pair of piezoelectric members along an electrode surface to form a common electrode between each pair, and   a source of alternating electrical potential coupled to said electrode surfaces.   
     
     
       12. The apparatus of claim 11 wherein said source of alternating electrical potential is coupled to said transducer such that one terminal of said source is attached to each of the common electrodes of said bimorph elements and the other terminal of said source is attached to each of the remaining electrode surfaces on the piezoelectric members. 
     
     
       13. The apparatus of claim 9 wherein the plurality of bimorph elements are stacked to form a substantially rectangular transducer configuration having a substantially planar surface parallel to the direction of electrical polarization and perpendicular to the electrode surfaces, said planar surface forming the surface providing the shearing motion. 
     
     
       14. The transducer of claim 13 wherein the means for separating comprises a substantially uniform layer of high compliance material having opposed parallel planar surfaces rigidly attached to electrode surfaces of adjacent bimorph elements. 
     
     
       15. A method of generating shear waves comprising: forming a transducer having a plurality of bimorph elements each separated by a compliant material;   placing said transducer in contact with a material in which it is desired to induce shear waves; and   applying an electrical potential to said bimorph elements so as to cause said bimorph elements to generate a shear wave in said material.